1. Field of the Invention
The present invention relates generally to a method of use and manufacture of an orthopedic implant, and, more particularly, but not by way of limitation, to an orthopedic implant that features a lower profile, beveled edges, and more strength than conventional orthopedic implants.
2. Description of the Related Art
Common orthopedic implants for use in fixating bones together include orthopedic staples. Conventional orthopedic staples have a bridge that connects two or more legs. To fixate bones during surgery, the surgeon drills holes in two bones, or two bone fragments, and then inserts the legs of the orthopedic staple into the holes. The legs can be smooth or have barbs to resist pull out from the bone. Orthopedic implants for use in fixating bones together include several types. Conventional rigid orthopedic staples have a bridge connecting two or more legs and do not create any lasting compression of the two bones. Improvements on conventional rigid orthopedic staples are orthopedic staples made from a shape memory material such as nitinol.
Orthopedic staples made from a shape memory material include a bridge connecting two or more legs wherein the legs converge towards one another at the tips. The advantage of shape memory orthopedic staples is that they can create lasting compression between bones or bone fragments. Specifically, shape memory orthopedic staples can be temporarily distorted within their elastic strain limits so that the legs are parallel. Having the legs parallel allows the staple implant to be inserted into two bones or bone fragments. After insertion and upon release, and, if necessary upon heating to the proper temperature, the implant will return to its converging shape and thus squeeze the two bones or bone fragments together thereby creating lasting compression.
FIGS. 1-6 illustrate a prior art shape memory implant 10. The bridge 3 of the implant 10 has four surfaces, a top surface 20, two side surfaces 21 and 22, and a bottom surface 23. The top surface 20 has a surface normal that points upwards, the bottom surface 23 has a surface normal that points downwards, and the side surfaces 21 and 22 have surface normals that are directed orthogonal to the surface normal of top surface 20. FIGS. 1 and 2 illustrate the implant 10 in an insertion position 100 with legs 1 and 2 parallel to each other and perpendicular to a bridge 3. As illustrated in FIG. 2, angle alpha is approximately 90 degree in the insertion position 100. Furthermore, in the insertion position, the bridge 3 is a uniform height from corner 4 to corner 5.
FIG. 3 illustrates the implant 10 in an implanted position 150 wherein leg tips 6 and 7 of the legs 1 and 2 are closer together than the insertion position 100. Specifically, the corners 4 and 5 produce rotational torque to squeeze the tips 6 and 7 together thereby creating a compressive force between the legs 1 and 2. Furthermore, in the implanted position, the bridge 3 of implant 10 is slightly arched helping to create a compressive force between legs 1 and 2.
Whether the implant 10 is in the insertion position 100 or the implanted position 150, the bridge 3 of the implant 10 has a uniform thickness from end to end. FIGS. 4 and 5 illustrate a top view and a side view of the implant 10 showing the bridge 3 has an approximate rectangular cross-section. In particular, the cross-section of the bridge 3 is uniform from a corner 4 to a corner 5 and across the length of the bridge 3. The uniform thickness from end to end of the bridge 3 creates sharp edges that may be felt as a rectangular lump by the patient after surgery.
FIG. 6 illustrates the implant 10 implanted into a bone 200. The implant 10 is placed into the insertion position 100 and inserts into the bone 200. The implant 10 then moves from the insertion position 100 to the implanted position 150 due to stored energy in the shape memory implant 10. After the implant 10 is implanted into the bone 200 the top surface 20 of the bridge and the side surfaces 21 and 22 form a rectangular lump that would be present on top of the bone 200 and under the soft tissue of a patient.
FIGS. 7-9 illustrate a prior art shape memory implant 50 disclosed in U.S. Pat. No. D705,930S. The implant 50 includes legs 56 and 57 connected with abridge 51. The bridge 51 of the implant 50 has four surfaces, atop surface 52, two side surfaces 53 and 54, and a bottom surface 55. The top surface 52 has a surface normal that points upwards, and the bottom surface 55 has a surface normal that points downwards. The top surface 52 is wider than the bottom surface 55 such that the side surfaces 53 and 54 taper from the top surface 52 towards the bottom surface 55. As a result, the bridge 51 is wider than the legs 56 and 57, which increases the strength of the implant 50.
FIGS. 7-9 illustrate the implant 50 in an implanted position wherein leg tips 59 and 60 of the legs 56 and 57 are closer together than in an insertion position where the legs 56 and 57 are parallel to each other and perpendicular to abridge 51. Specifically, in the implanted position, the corners 61 and 62 produce rotational torque to squeeze the tips 59 and 60 together thereby creating a compressive force between the legs 56 and 57. Furthermore, in the implanted position, the bridge 51 of implant 50 is slightly arched helping to create a compressive force between legs 56 and 57.
Whether the implant 50 is in the insertion position or the i ted position, the bridge 51 of the implant 50) has a uniform thickness from end to end. In particular, the cross-section of the bridge 51 is uniform from the corner 61 to the corner 62 and across the length of the bridge 51. The uniform thickness from end to end of the bridge 51 creates edges that may be felt as a lump by the patient after surgery.
FIG. 10 illustrates a prior art implant 610 in an insertion position 750. The implant 610 includes a bridge 605 and four legs 601-604. The bridge 605 spans and connects the four legs 601-604 at corners 606-609. The bridge 605 of the implant 610 has a uniform height between the four legs 601-604, and the top surface has a normal that is directed vertically upwards. The bridge 605 of the implant 610 has across-sectional profile that is substantially similar to the bridge 3 of the implant 10 in that the bridge 605 of the implant 610 has a uniform thickness from end to end. As such, the implant 610 like the implant 10 creates sharp edges that may be felt as a rectangular lump by the patient after surgery.
In addition to the prior art staple described above, there are other shape memory orthopedic staples on the market today. The Stryker Easy Clip™ implant is a nitinol implant with abridge connecting two converging legs. It is mechanically distorted so that the legs are in a parallel shape via a metal instrument. The same metal instrument is used to insert the legs into bone, and then releases the staple. U.S. Pat. No. 8,584,853 B2 and related U.S. Pat. No. D 705,930S, U.S. Pat. No. D691,720S, and U.S. Pat. No. D706,927S, as previously described with respect to FIGS. 7-9, are nitinol implants with a bridge that connects two or more converging legs. These implants are pre-loaded onto insertion tools that maintain the leas in parallel position for later insertion into bone. The Stryker Easy Clip™ and the products disclosed in U.S. Pat. No. 8,584,853 B2; U.S. Pat. No. D 705,930S; U.S. Pat. No. D691,720S; and U.S. Pat. No. D706,927S are examples of nitinol implants wherein the bridge has a uniform width and thickness across the entire implant. Specifically, a cross section taken orthogonal to the bridge at any location between the legs would show the same cross-section height.
There are various methods of manufacturing elastic shape memory implants such as the Stryker Easy Clip™ as well as the implants 10, 50, and 610. The Stryker Easy Clip™ can be manufactured by electrical discharge machining from a flat plate. The implants 10 and 50 can be manufactured by electrical discharge machining or a similar method from a billet. The implant 610 can be manufactured from a flat sheet of material. Specifically, the implant 610 is cut from a flat sheet and the legs 601-604 are then bent into the final shape. Regardless, of whether implants are manufactured using electrical discharge machining, or manufactured from a flat plate or billet of material, the implants 10, 50, and 610 feature a uniform bridge thickness such that the patient would feel the full thickness of bridge at all locations.
As described above, the existing prior art orthopedic implants have bridges with uniform thickness from end to end after they are manufactured. In particular, a cross section taken orthogonal to the bridge at any location between the legs would show the same cross-section height. This design can potentially create a bulge or protuberance after surgery that can be fell by a patient as a lump under their skin. After manufacture, and to mitigate the problems associated with having a bridge with uniform thickness, the edges of the prior a implants may he rounded by mechanical tumbling or acid etching. However, even after mechanical tumbling or acid etching the surfaces that make up the bridge are orthogonal to each other and the bridge still has a uniform thickness that can potentially be felt by a patient. Furthermore, mechanical tumbling or acid etching an implant after manufacture increases costs.
Accordingly, a shape memory implant design and a method of manufacture thereof that has a lower profile and tapered shape at the time of manufacturing, does not have orthogonal bridge surfaces, has greater strength than prior art implants, and creates less of a bulge or protuberance under the skin would be beneficial.